The instant invention relates to methods and apparatus for accurately aligning a length of optical fiber along an optical axis of a spherical lens, whereafter the lens and fiber are joined together to provide a pigtailed lens assembly for a fiber optic cable.
The prior art teaches iterative micropositioning of the end of an optical fiber relative to the focal point of a lens to achieve a collimated light beam whereupon the fiber is bonded to the lens with a suitable adhesive. For example, U.S. Pat. No. 4,509,827 to Cowen et al. and U.S. Pat. No. 4,545,643 to Young et al. teach methods for fabricating fiber optic connectors having an optical fiber abutting a graduated refractive index (GRIN) rod lens wherein a mirrored surface is positioned substantially orthogonally relative to the axis of the lens in order to autocollimate a light beam transmitted therethrough. A light beam is thereafter transmitted through the fiber, and the fiber is iteratively micropositioned relative to the lens until the returning light signal is maximized. The fiber is then secured to the lens as by potting the abutting end thereof in a suitable adhesive. Accuracy is thus dependent on proper calibration of the mirrored surface, which calibration may be disturbed in the potting process.
Similarly, U.S. Pat. No. 4,637,683 to Asawa teaches a method for aligning optical fiber connectors wherein an optical fiber is iteratively micropositioned relative to one end of a GRIN lens so as to maximize the reflection of light emanating from the fiber back from the opposite end of the lens. Significantly, the method requires a coating step to create the reflective surface on the opposite end of the lens, which is introduced into the optical path, as well as the creation of a reference plane to ensure a proper angle of incidence for light rays.
Alternatively, the prior art teaches the use of special lens assemblies which facilitate the alignment of optical fibers therewith. For example, U.S. Pat. No. 4,666,238 to Borsuk et al teaches a lens assembly having a rearward extension for aligning and retaining the end of an optical fiber at the focal point thereof. Borsuk et al thus necessitates the use of specialized lens assemblies requiring strict manufacturing tolerances for successful alignment of the fiber with the focal point of the lens. Still further, the Borsuk method fails to provide convenient means for checking the coupling efficiency achieved between the fiber and lens, and the improper bonding of the fiber to the lens will result in the discarding of a part (the lens) for which much cost has already been incurred.
Thus, the prior art teaches methods for bonding an optical fiber to a lens involving complex reflection schemes which are critically dependent upon the proper calibration of reference surfaces or planes to achieve proper fiber/lens alignment, which calibration may be jeopardized during the joining stage as when applying adhesive between the fiber and the lens. Alternatively, the prior art teaches the use of costly specialized lens assemblies to facilitate the alignment and joining of an optical fiber to the focal point of a lens. It is further noted that, where a pigtailed lens assembly employing a spherical lens is desired, the prior art fails to provide means for rotationally manipulating the lens prior to joining an optical fiber therewith so as to maximize coupling efficiency should the lens have a crystal structure which provides a unique optical axis of maximum transmissivity. Finally, prior art methods for fabricating pigtailed lens assemblies fail to provide convenient means for testing the coupling efficiency achieved between the fiber and lens thereof immediately subsequent to the joining of the fiber and lens.